2.  An Internet address is made of four bytes (32 bits) that define the host connection to a network.  It is uniquely and universally defines the connection of a host or a router to the internet.

3.  Two Types:  Classful Addressing  Classless Addressing

4.  Five Types:  Class A ( Unicast)  Class B (Unicast)  Class C (Unicast)  Class D ( Multicast)  Class E ( Future Use)

5.  Unicast: Communication from one source to one destination.  Multicast: Communication from one source to a group of destination  Broadcast: Communication from one source to many destinations, which are in same network.

6.  Binary Notation: 4 bytes (32bits) binary number 10000000 00001011 00000011 00011111  Decimal Notation: Internet address are usually written in decimal form with decimal point separated the bytes.

7. Finding the Class in Binary Notation

8. Finding the Class in Dotted – Decimal Notation

9.  In classful addressing each class is divided into fixed of blocks.

10.  All hostid bytes are 0s.  The network address defines the network to the rest of the Internet.  The network address is the first address in the block.  Given the network address, we can find the class of the address.

11. A Network with Two Levels of Hierarchy

12. Addressing without Subnets

13. Network and Host Addresses

15. A Network with Three Levels of Hierarchy

17. Addresses with and without Subnetting

20.  A network administrator knows the network address and subnet address, but a router doesnot. The router outside the organisation use a default mask; the router inside the organisation use a subnet mask.  A 32 – bit number called the mask.  Two types:  Default mask ( Identify the network address) Class A 255. 0. 0. 0 /8 Class B 255.255.0.0 /16 Class C 255. 255. 255. 0 /24  Subnet mask ( Identify the subnet address)

21.  A bitwise AND operation between IP address and default mask yields a network address.  Note that zeros bit are used to mask out the host number resulting the network address.  Example: IP Address: 190. 240. 7. 91 Default Mask: 255. 255. 0. 0 Network address: 190. 240. 0. 0

22.  The number of 1’s in a subnet mask is more than the number of 1’s in the corresponding default mask.  In other words, in a subnet mask, we change some of the Rightmost 0s in the default mask to make a subnet mask.  The number of subnets is determined by the number of extra 1s. If the number of extra 1s is n, the number of subnets is 2 to the n.  A bitwise AND operation between IP address and subnet mask yields a subnet address.  Example: IP Address: 190. 240. 33. 91 Subnet Mask : 255. 255. 224.0 /19 Subnet address: 190.240. 32. 0

23.  The idea of classful addressing has created many Problems. Until mid – 1990’s, a range of address meant a block of addresses in class A,B,C.  The minimum number of address granted to an organization was 256 ( Class C); the maximum was 16,777,216 (Class A).  In addition what about a small business that needed only 16 addresses?  During 1990s, ISP came into prominence. An ISP can be granted several class B or Class C blocks and then subdivide the range of addresses in group of 2, 4, 8, or 16 address), giving a range to a household or a small business. This is called the classless address.

24.  A better way to define a block of addresses is to select any address in the block and mask. A mask is a 32 bit number in which the n leftmost bits are 1s and the 32 – n rightmost bits are 0s. However, in classless addressing the mask for a block can take any value from 0 to 32. Address: 205.16.37.39/28 11001101 00010000 00100101 00100111 Mask : 11111111 11111111 11111111 11110000 First address( Network address): 11001101 000100000 00100101 00100000 Address: 205.16.37.39/28 11001101 00010000 00100101 00100111 Mask complement : 00000000 00000000 00000000 00000111 Last address : 11001101 00010000 00100101 00101111 Number of addresses in a block: 2 32-28 =2 4 = 16

25.  In 1987, RFC 1009 specified that a subnetted network could use more than one subnet mask.  When an IP network is assigned more than one subnet mask, it is considered a network with variable length subnet masks.

26. 26  Benefits › Efficient use of the organization’ s assigned IP address space.

27. 27  Assume that a network administrator has decided to configure the 130.5.0.0/16 network with a /22 extended-network prefix.  This disign allows for 64 subnets with 1,022 hosts each.  Fine if the organization plans to deploy a number of large subnets.  What about the occasional small subnet containing only 20 or 30 hosts?  About 1,000 IP host addresses wasted for every small occasional subnet!

28. 28  Assume in previous example that administrator is also allowed to configure the 130.5.0.0/16 network with a /26 extended-network-prefix.  /26 permits 1024 subnets with 62 hosts each.  The /26 prefix would be ideal for small subnets with less than 60 hosts, while /22 prefix is well suited for larger subnets up to 1000 hosts.

29. Addresses for private networks

30. A NAT implementation

31. 19.31 Addresses in a NAT